Hair styling and treatment systems use high concentrations of caustic and/or reducers and oxidizers to permanently wave or straighten the hair by rearranging disulfide linkages. The Brazilian keratin method uses free aldehydes, like formaldehyde, gluteraldehyde or other mono and dialdehydes to crosslink or bind hydrolyzed proteins to the hair cuticle. Recent improvements, like the Coppola method in United States Patent Application 20090211593, complexes aldehydes in Schiff-base or other similar reactive keratin complexes that initially have lower free aldehyde present, but always contain some free aldehydes in the formulation prior to being applied to hair. Furthermore, the nature of the complexed aldehydes allows for a significant amount of aldehyde to be released during the thermal process of flat ironing the hair. Long term occupational exposure to aldehydes is generally considered undesirable. Scalp exposure to aldehydes and other treatment chemicals also may induce allergic reactions or irritation to individuals. One treatment method often referred to as the Japanese treatment, for example, relies on lye and other harsh chemicals and is very high in pH.
Mercapto-silicones of specific amounts of functionality have been used in hair care treatments as conditioners and styling aids, and even as intermediates for creating new styling polymers. U.S. Pat. No. 6,562,324 to Kumar et al, published May 13, 2003 required the free radical polymerization of ethylenically unsaturated monomers with a mercapto functional silicone as a chain transfer agent, thus forming an acrylate grafted polymer for improved curl retention as a fixative. No mention of high temperature thermal styling using a mercapto siloxane alone is provided. Kumar references the required number of mercapto functional groups on the mercapto functional silicone compound that will be reacted with monomers to form a graft polymer. It that invention, only the graft polymer serves as a styling aid, not a free mercapto siloxane. Furthermore, the —SH number reference is interpreted to be the relative number of SH groups acting as a chain transfer agent, thus implying that significantly less or no free mercapto functionality is remaining after the free radical polymerization is completed. Kumar further states if the number of mercapto functional groups on the mercapto functional silicone compound is too high, desired properties such as desirable sensational feeling in makeup cosmetics, and soft feel in hair care cosmetics will be lost. If the number of mercapto functional groups on the mercapto functional silicone compound is too low, desired properties such as style retention properties in hair care compositions may not be obtained. Lastly, it is taught that the SH equivalent weight of the mercapto functional silicone compound used as a chemical intermediate in free radical polymerization of ethylenically unsaturated monomers is preferably between 400-4000, and more preferably 1000-2000 and wherein the mole ratio of “silicone” monomer to “mercapto functional” silicone monomer “m/n” is 9-49. For such polymers, the description of desired property set is not directed to the intermediate mercaptan functional polymer, but rather to the acrylate-grafted mercaptan functional polymer of the invention.
Fridd in EP0295780 and Gee in EP-0829257 teach the use of mercapto functional silicones (non-modified) as an additive when treating hair with a composition containing an agent effective in reducing the disulphide linkages therein, e.g. ammonium thioglycollate. The hair is then arranged in the desired configuration and the disulphide linkages restored by application of an oxidizing agent. These methods require the redox cycle and also expose the scalp to high pH conditions.
Therefore alternative treatment methods are needed that produce excellent permanent or semi-permanent straightening results without damage to the hair, that are completely aldehyde-free, pH balanced to the scalp and do not have to rely on any harsh chemicals such as lye or a two part redox treatment to break and/or set disulfide linkages in the hair cortex.